Okay, not really aliens. The Kuiper Beasts came from somewhere else originally, but that was a long time ago; they have been living in the Solar System since the late Precambrian. It turns out that most main sequence stars have a halo of icy objects; this is the KB's niche, all across the galaxy and possibly beyond.
(Yes, this is sort of a James Nicoll thread.)
The KBs perfect habitat would be a small, cold, icy moon with an ambient temperature around 30 degrees absolute and low (<tenth of a gee) surface gravity. They're adaptable, though, and can live almost anywhere that's under 100 absolute. Saturn is right at the edge of this, but the KBs keep a lot of industrial base there because the energy flux is so high. They never come further in towards the Sun, though they could send robots if they really wanted to.
So, POD 1979: Pioneer 11 sends back photos showing all sorts of stuff going on: factories, big slow starships and tugs, solar panel arrays, you name it. Frantic attempts to contact the "aliens" follow.
A problem is that the KBs have close to zero interest in small hot rocky worlds or the things that live on them. One reason is that they're almost entirely lacking in abstract curiosity. Another is that their long long history tells them getting too friendly with hotlife tends to end badly -- usually with the hotlife getting uppity and having to be sharply rebuked. Since the Beasts are heirs to several hundred million years of technological progress, rebukes can be dismayingly permanent.
So KB responses tend to be few, short, and to the point: Yes, we know you're there. No, we're not interested in talking. Please don't bother us.
That said, they don't mind an orbiter or two floating around Saturn as long as it doesn't get in the way. A good enough orbiter may provide some interesting insights; KB technology doesn't violate or severely bend any laws of nature (no antigrav, total conversion, or FTL) but it's very very advanced, and some of the works around Saturn are using very large amounts of energy and mass to Do Stuff.
Nearly thirty years after initial contact, though, they still have no interest in talking to us.
Thoughts? Consequences for human culture? Technology, philosophy, religion?
Doug M.